Determination of the mechanical behavior and physical properties of materials is necessary so that materials may be selected for use, evaluated when in use, and evaluated after use. From these determinations, decisions are made as to which materials to use, the conditions under which they can be used, and whether such materials in use can be continued to be used with safety. These types of determinations are particularly useful for determining the effects of environmental loading such as nuclear radiation, temperature, water chemistry, and force on the mechanical properties of in-service materials.
While not limited to the field of determining the effects of nuclear irradiation and environment on the mechanical properties of materials, the impetus for the invention originated with the needs and necessities of this activity. The invention is fully applicable to the determination of mechanical behavior of materials not subjected to radiation, and the validity of the invention was demonstrated for materials not subjected to radiation.
In the past, the most common procedure has been to determine the mechanical behavior of a material by testing large samples that are created more or less simultaneously or "side by side" with the product that is intended to be used. In determination of the mechanical behavior of solid materials, and particularly metals, the practice is to make tensile, stress-corrosion cracking, S-N fatigue, creep, stress relaxation, ductile/brittle transition, compact tension, fracture mechanics, fatigue crack initiation/propagation, fracture modes, fracture stress/strain, multilayered, residual plastic stress/strain, ion irradiated, etc. specimens, and these are then subjected to forces, displacements, or both using conventional screw driven or servohydraulic testing machines while measurements are taken of the force, time, displacement, impact energy decrement, velocity, crack propagation, etc. of the specimen. Information such as stress and strain, which can be thought of as normalized load and deflection respectively, and crack length are then obtained by simple mathematical operations and previous calibrations. For example, in a uniaxial tensile test, the stress is determined by dividing the measured load by the specimen cross sectional area. In a fracture mechanics test, the crack extension is determined by visual examination, or by the electric potential method, or the unloading compliance method, or any combination of these methods.
While the common procedure to determine mechanical behavior of materials may be satisfactory in some instances, there are other circumstances where it is desirable to load, displace, or both load and displace specimens in a hostile environment using remotely controlled load, displacement, or both load and displacement. This approach is particularly effective in characterizing the phenomenon of corrosive attack, such as stress-corrosion cracking (SCC). When studying SCC in the laboratory, it is often difficult to simulate the actual in-service environment. Thus, it is of great importance to be able to load, displace, or both load and displace specimens, components, and systems remotely during actual in-service operation.
The present invention was conceived as a solution to the problem of determining SCC behavior in power plants during full power operation. There are five principal conceptual innovative aspects to the method for remote application of load, displacement, or both to specimens, components, or systems. The first is the use of an expandable, contractible, or both expandable and contractible (displaceable) container with a heating or heating and cooling element capable of heating or heating and cooling a solid material inside the container. The second is the use of a solid material force/displacement exerting member, of sufficient size to contact ends of the container, inside the container which is capable of expanding upon heating, contracting upon cooling, or both. The third is to modify the load exerted by the container, to modify the displacement of the container, or both by heating or heating and cooling the element and solid force/displacement exerting expansion/contraction material. This process results in the expansion or contraction of the container. The fourth is to attach the container to the specimen, component, or system and to apply load, deflection, or both. The fifth is to modify the heating or heating and cooling applied to the force/displacement exerting member in a controlled manner to obtain a desired load, deflection, or both.
There are several important advantages of the invention described here over the approach which uses fluid pressurization to expand a bellows. The first is that only solid wire penetrations of the nuclear reactor primary system are needed for the electrically heated solid material variable load system to function. Fluid carrying penetrations present a more direct threat to depressurizing the reactor coolant system during operation. Another important advantage of the solid material force/displacement exerting invention is that active valves are not required to equalize displacement during nuclear reactor plant startups or transients. Another advantage of the solid material force/displacement exerting invention is the superior load/displacement control which can be achieved as compared to fluid systems which experience longer feedback effects and instability due to fluid boiling.